Effect of salinity on diazotrophic activity and microbial composition of phototrophic communities from Bitter-1 soda lake (Kulunda Steppe, Russia)

Abstract

Bitter-1 is a shallow hypersaline soda lake in Kulunda Steppe (Altai region, Russia). During a study period between 2005 and 2016, the salinity in the littoral area of the lake fluctuated within the range from 85 to 400 g/L (in July of each year). Light-dependent nitrogen fixation occurred in this lake up to the salt-saturating conditions. The rates increased with a decrease in salinity, both under environmental conditions and in laboratory simulations. The salinities below 100 g/L were favorable for light-dependent nitrogen fixation, while the process was dramatically inhibited above 200 g/L salts. The analysis of nifH genes in environmental samples and in enrichment cultures of diazotrophic phototrophs suggested that anaerobic fermenting and sulfate-reducing bacteria could participate in the dark nitrogen fixation process up to soda-saturating conditions. However, we cannot exclude the possibility that haloalkaliphilic nonheterocystous cyanobacteria (Euhalothece sp. and Geitlerinema sp.) and anoxygenic purple sulfur bacteria (Ectothiorhodospira sp.) might also play a role in the process at light conditions. The heterocystous cyanobacterium Nodularia sp. develops at low salinity (below 80 g/L) that is not characteristic for Bitter-1 Lake and thus does not make a significant contribution to the nitrogen fixation in this lake.

Metagenomes and metatranscriptomes shed new light on the microbial-mediated sulfur cycle in a Siberian soda lake

“…The latter family members might be reversed acetogens, able to oxidize acetate in syntrophy with methanogens or SRB, or they might be hydrogenotrophic acetogens [35, 41]. The most abundant 16S rRNA gene transcripts were assigned to Nodosilinea (relative abundance ~ 17%; a genus of haloalkaliphilic, filamentous benthic Cyanobacteria [42, 43]) in the 0–2-cm layer of sediments and to Nitriliruptoraceae (~ 17%; a family of putative nitrile-hydrolyzing Actinobacteria [44]) in the 2–4-cm layer (Additional file 5: Figure S3), groups from which we recovered 1 and 38 different MAGs, respectively (Additional file 4: Dataset 1).

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Salt-dependent succession of phototrophic communities in the soda lake Tanatar VI (Altai Region, Russia)

“…Thus, the ecosystem of soda lake Tanatar VI includes water body, its littoral area and surrounding soils. Tanatar VI represents a highly dynamic ecosystem with long-standing fluctuations of salinity, which cause succession of phototrophic communities that was not observed in the other studied soda lakes of this region (Namsaraev et al, 2018;Samylina et al, 2019).…”

“…Samples of phototrophic biomass were collected from the brine, littoral area, and surface of the moist soil surrounding the lake. Salinity, pH, soluble carbonate alkalinity and potential nitrogen fixation (NF) measurements, as well as identification of algae and cyanobacteria, were performed similarly to previous studies (Samylina et al, 2014;2019;Namsaraev et al, 2018).…”

“…There are soda lakes among them, which maintain stable alkaline pH due to a prevalence of soluble carbonates in the brines. Thereby diversity and functioning of phototrophic communities of unique soda lakes are actively studied in recent years (Samylina et al, 2014;2019;Namsaraev et al, 2018). Ecosystem of Tanatar VI possesses some peculiarities which distinguish it from the previously studied lakes.…”

Isachenkonia alkalipeptolytica gen. nov. sp. nov., a new anaerobic, alkaliphilic proteolytic bacterium capable of reducing Fe(III) and sulfur

“…Recent microbiological studies of Kulunda steppe soda lakes have led to the isolation of several new taxa of alkaliphilic prokaryotes [18–27] and to the characterization of various microbial processes taking place in these habitats [28–39]. In particular, it was shown that the dead biomass of the primary producers could serve as a source of proteins and peptides for numerous proteolytic bacteria, including members of the phylum Firmicutes Proteinivorax tanatarense [40, 41] and Proteinivorax hydrogeniformans [42] or Candidatus ‘Cyclonatronum proteinivorum’ of the phylum Balneolaeota [43].…”